The invention relates to a process for producing a metal-ceramic substrate for electric circuits or components. At least one side of the ceramic layer is provided with at least one structured metal layer. A second metal layer is applied to the first structured metal layer by electroless chemical deposition.
Producing a metal coating necessary for manufacturing printed circuits, terminals, etc. on a ceramic, for example on an aluminum oxide ceramic with the so-called "DCB process" (direct copper bond technology) using metal, or copper foils, or metal, or copper sheets, which form the metal coating and which on their surface sides have a layer or a coating (melted-on layer) of a chemical compound of the metal and a reactive gas, preferably oxygen, has been undertaken. In this process, which is described for example in U.S. Pat. No. 3,744,120, or in U.S. DE Pat. No. 2,319,854, this layer or coating (melted-on layer), forms an eutectic with a melting point below the melting point of the metal (for example, copper) so that by placing the foil on the ceramic, and by heating all the layers, they can be joined to one another by melting on the metal, or copper, in the area of the melted-on layer, or oxide layer.
This DCB process has the following process steps, for example:
oxidizing a copper foil such that a uniform copper layer results; PA1 placing the copper foil on the ceramic layer; PA1 heating the composite to a process temperature between roughly 1065.degree. C. and 1083.degree. C., for example to roughly 1071.degree. C.; PA1 cooling to room temperature.
Furthermore, it is known to use laser machining, or treatment, of the ceramic (for example, Guenter Spur Machining of Ceramics, Hauser Verlag, ISDN 9-446-15620-8).
Previously, the ceramic is either cut, or blind hole-like depressions are made in the ceramic by individual pulses, for example, for producing scored lines on which a multiple substrate can be separated into individual substrates by breaking. However, laser treatment can be used for other purposes. The spacing of the holes is, for example 0.1-0.5 mm and the penetration depth of treatment is between 2-70% of the ceramic thickness.
For example, CO.sub.2 lasers or Nd-YA6 lasers are suited for laser machining.
Production of metal-ceramic substrates with laser-treated ceramic layers is accomplished as follows, especially when using the DCB process: First, the bare ceramic layer, i.e. not yet provided with a metal layer, is treated using the laser along the desired scored lines. Then the first metal layers are applied, for example in the form of copper foils, and using the DCB process, or an active soldering process. In another process step, this first metal layer is structured in the required manner using known etching and masking techniques, in which first an etching mask is produced, for example by stencil printing, or photoprinting, and then, the required structuring or the required layout is produced using this mask by etching.
Another metal layer is then produced on the structured first metal layer, for example, by electroless chemical deposition in the corresponding baths.
Along the scored lines produced by laser machining, the multiple substrate can be divided into the individual substrates by breaking.
The known process in which laser machining is done before applying the metal coating has the defect that at the start of the production process, product-oriented laser machining of the ceramics is necessary and thus also product-oriented storage is necessary, with the disadvantage of high storage costs and long passage times. Furthermore, there is the danger that the respective laser-treated bare ceramic will break in an unwanted manner during application of the first metal layers or during the handling necessary for this purpose.
If laser machining is done as the last step at the end of the production process, i.e. after electroless chemical deposition of the second metal layers, this has the defect that the substrate surface is highly fouled by the plasma which is released in laser machining. Longer residence times and/or heating during laser machining can also lead in an undesirable manner to corrosion of the surface of the metal coatings formed by the metal layers; this adversely affects further use of the substrate, for example, leading to reduced solderability or wire bondability of the surface of the metal coatings.
Attempts to undertake laser machining after structuring of the first metal surfaces and before electroless or chemical application of the other metal layers have not lead to any useful results to date. In particular, it has been found that metal is deposited in electroless chemical deposition on the edges and on the bottom of the scratches, or notches, or holes, produced by laser machining. This undesirable metal coating, which is located on the edge of the individual substrates, after separating the multiple substrate into the individual substrates, leads to a reduction of the dielectric strength between the top and bottom of the individual substrates.
It is an object of the invention is to devise a process which avoids the defects of the known processes, especially expensive product-oriented storage of ceramics.